Add fullscreen in-app image view, no stretch, sharing the editor's in-app/external toggle

ImageView.py

@@ -0,0 +1,41 @@
+"""Fullscreen in-app image view (Features/Major: "Different display in
+middle" — fullscreen image, no stretch). Fills Browser's file-area Container
+in place of the entry list, same mechanism as Editor.py's EditorView. Just
+fit-to-window display — no zoom/pan, matching what was actually asked for."""
+
+from pathlib import Path
+from typing import Callable
+
+import flet as ft
+
+from Core import Palette
+
+
+class ImageView(ft.Container):
+    def __init__(self, EntryPath: Path, OnClose: Callable[[], None]):
+        self.EntryPath = EntryPath
+        self.OnClose = OnClose
+
+        Toolbar = ft.Row(
+            [
+                ft.IconButton(
+                    icon=ft.Icons.ARROW_BACK, tooltip="Back to file list", on_click=lambda e: self.OnClose()
+                ),
+                ft.Text(EntryPath.name, weight=ft.FontWeight.BOLD, expand=True),
+            ],
+            spacing=8,
+        )
+        Body = ft.Container(
+            content=ft.Image(src=str(EntryPath), fit=ft.BoxFit.CONTAIN, expand=True),
+            expand=True,
+            padding=12,
+        )
+
+        super().__init__(
+            content=ft.Column(
+                [Toolbar, ft.Divider(height=1, color=Palette.Surface1), Body], expand=True, spacing=8
+            ),
+            expand=True,
+            bgcolor=Palette.Base,
+            padding=12,
+        )